(nin-juh up) verb. The act of tying a black t-shirt to ones face and doint subversive activities. Usually used when stealing cigarettes or blowing up peoples cars.
Johnny Twobags - Man, Ame has a pack of Newports, but shes asleep and I'd have to crawl over her.
Mr. Dopey - You'd better ninja up and do that shit
*Johnny Twobags ties his shirt up and backflips off the ceiling.